1. Field of the Invention
The present invention relates to an image projection apparatus such as a projector.
2. Description of the Related Art
Heretofore, there has been known an image projection apparatus including a DMD (Digital Mirror Device) serving as an image generating element that generates an image based on image data supplied from a personal computer or the like; an lighting unit that irradiates the image generating element with light from a light source; and a projection optical system for forming an optical image, which is generated by the image generating element and the lighting unit, on a projection plane (for example, Japanese Patent Application Laid-open No. 2008-134432).
Specifically, the light from the light source which travels in parallel with an image generation surface of the DMD is reflected toward the image generation surface of the DMD by an illumination optical system, such as a reflection mirror, and is applied onto the image generation surface of the DMD. On the imaging generation surface of the DMD, a plurality of movable micromirrors is arranged in a lattice. Each micromirror allows the mirror surface thereof to be inclined about a torsion axis by a predetermined angle, and allows the mirror surface to have two states of “ON” and “OFF”. When the micromirror is in the “ON” state, the micromirror reflects light from the light source toward the projection optical system. When the micromirror is in the “OFF” state, the mirror reflects the light from the light source toward a light absorber provided in the apparatus. Accordingly, individually driving the mirrors makes it possible to control the projection of light for each pixel of image data and to generate an optical image. The optical image generated by the DMD passes through the projection optical system and is formed on the projection plane.
Additionally, Japanese Patent Application Laid-open No. 2008-250277 discloses an image projection apparatus including a projection optical system composed of a first optical system formed of a plurality of lenses and a second optical system including a concave mirror. In the image projection apparatus disclosed in Japanese Patent Application Laid-open No. 2008-250277, the first optical system forms an intermediate optical image conjugate to the optical image generated by the image generating element between the first optical system and the second optical system, and the second optical system enlarges and projects an image conjugate to the intermediate optical image the intermediate optical image on the projection plane. The configuration of the projection optical system as described above achieves point-blank projection.
FIG. 17 is a diagram illustrating a usage example of the image projection apparatus disclosed in Japanese Patent Application Laid-open No. 2008-250277.
As illustrated in FIG. 17, in the image projection apparatus disclosed in Japanese Patent Application Laid-open No. 2008-250277, the optical image generated by an image generating element 12 advances in a direction orthogonal to a projection plane (screen) 101, passes through a first optical system 70, and is reflected by a concave mirror 42 serving as the second optical system and projected on the projection plane.
As illustrated in FIG. 17, the image projection apparatus is generally used in the state of being placed on a desk 100 or the like which is opposed to the projection plane 101. The desk, chair, and the like used by a user are also arranged to be opposed to the projection plane 101. As disclosed in Japanese Patent Application Laid-open No. 2008-250277, an image projection apparatus 1A in which the image generating element 12, an illumination unit 20, and the first optical system 70 are arranged side by side in series in the direction orthogonal to the plane of a projected image projected on the projection plane 101 is elongated in the direction (X-direction in the figure) orthogonal to the projected image plane. Thus, when the image projection apparatus 1A is elongated in the direction orthogonal to the projected image plane, an installation space for the image projection apparatus 1A is required in the direction orthogonal to the projection plane 101. As a result, in a narrow indoor space, a sufficient space cannot be secured in the direction orthogonal to the projection plane 101, and the layout space for the desk and chair used by the user is limited. This results in a problem of impairing the convenience. Note that the phrase “arranged side by side in series” described above and below refers to an arrangement in which, on an optical path of outgoing light of an optical system formed of a certain optical element or a plurality of optical elements, the incidence plane of another optical system formed of another optical element or a plurality of optical elements is arranged.
In the above description, the case where the image projection apparatus is used by being placed on the desk 100 or the like has been described. However, even in the case where the image projection apparatus is used by being hung from the ceiling or the like, when the image projection apparatus is elongated in the direction orthogonal to the projection plane 101, the convenience is impaired for the following reason. That is, in the case of installing the image projection apparatus on the ceiling, the image projection apparatus may interfere with lighting equipment or the like arranged on the ceiling, so that the installation space for the image projection apparatus is limited and the convenience is impaired.
The present invention has been made in view of the above-mentioned problem, and it is an object of the present invention to provide an image projection apparatus capable of shortening the length in the direction orthogonal to the projection plane of the apparatus, as compared with the related art.